Automatic volume control with noise suppressor



API 20, 1937- w. L cARLsoN ET AL. 2,078,055

AUTOMATIC VOLUME CONTROL WITH NOISE SUPPRESSOR April 20, 1937. W CARLSQNET AL 2,078,055

AUTOMATIC VOLUME CONTROL WITH NOISE SUPPRESSOR Filed Dec. 22, 1932 2Sheets-Sheet 2 INVENTORS WENDELL l.. CARLON Patented pr. 20, 1937TUNITED STATES AUTOMATIC VOLUME CONTROL WITH NOISE SUPPRESSOR Wendell L.Carlson, Haddoneld, and Loren R. Kirkwood, Merchantviile, N. J.,assignors to Radio Corporation of America, a corporation of DelawareApplication December 22, 1932, Serial No. 648,422

35 Claims. (Cl. 25d-20) The present invention relates to radio receiversemploying automatic volume control circuits, and more particularly toreceivers embodying inter-channel noise suppressor arrangements.

In a co-pending applicationof K.` A. Chittick and W. L. Carlson, SerialNo. 642,544, led November lei, 1932, there have been disclosed automaticvolume control circuits for use in radio receivers. The characteristicfeature of the circuits disclosed in the said application comprised anautomatic volume control circuit which divided from the. sound channelat the grid of the last intermediate frequency amplifier stage, thevolume control circuit consisting of an intermediate frequency amplifierand a rectifier, the output electrode of the rectifier being connectedby a direct current path to the radio frequency, first detector andintermediate frequency stages for gain control of these stages. It waspointed out in the aforesaid application that one of the advantagesresulting from the arrangement shown therein was the reduction ofoverloading on the side of strong carriers due to the fact that therewas less selectivity to the volume control circuit than to the audiodetector. In other words, unlike the old volume control systems whichrequired a slight increase in signal potential to operate the volumecontrol tube, the system of the aforesaid application operated tocontrol the signal channel to a greater extent than the chan` nelsupplying the volume control tube.

Now, it is often desirable to embody in a receiver of the type.disclosed in the aforementioned application, an arrangement` capable ofproviding inter-channel noise suppression. The function of a noisesuppressor circuit is to reduce receiver noises, by greatly decreasingthe sensitivity of the receiver when no signal modulated carrier wavesare being received. Furthermore, it is highly desirable to achieve thefunction of noise suppression without introducing distortion of thesignals transmitted through the receiving system.

Accordingly, it may be stated that it is one of the main objects of thepresent invention to provide in a radio receiver, equipped with anautomatic volume control circuit, a noise suppressor system whosecircuits are confined entirely to the intermediate frequency circuits,and are not associated with the audio detector or audio circuits, thusresulting in smoother operation and no distortion at the thresholdoperating point.

Another important object of the present inf vention is to provide acircuit, for use in vconnection with the superheterodyne type of radioreceiver, which not only possesses the desirable features of anautomatic volume control system, but in addition thereto, includesinter-channel noise suppression, auxiliary means being provided foradjusting the degree of the suppression. The suppressor control isfurther characterized in that it is capable of functioning as a manuallyoperable sensitivity control to regulate the overall sensitivity of thereceiver, thereby eliminating the reception of signals having too greata noise level, and the suppressor control, additionally may include aswitch which is adapted to control the conductivity of the suppressortube whereby the suppressor action may be rendered effective orineffective at will.

Another object of the present invention may be said to consist in theprovision of an automatic volume control circuit for a radio receiver,which control circuit includes one network adapted to regulate the gainof at least one radio frequency stage in a manner such that the outputof the stage is substantially uniform regardless of variations in signalintensity in the input circuit of the stage, and an additional networkfor regulating the operation of the said radio frequency stage in such amanner that the stage is rendered inoperative to transmit electricalimpulses when the signal level in the input circuit of the stagedecreases below a predetermined intensity level.

Still another object of the present invention is to provide a radioreiver provided with means for automatically controlling the volume ofthe signal output therefrom, a manual volume control device beingdisposed in the audio frequency section of the receiver, and a manualsensitivity control device being disposed in a radio frequency sectionof the receiver, the sensitivity control being so arranged and connectedthat it is capable of regulating the suppression of noise or undesiredelectrical disturbances, the receiver being characterized by its freedomfrom noises between desired settings of the tuning device of thereceiver, said sensitivity control, additionally, including means foreliminating the aforesaid noise suppression function.

Still other objects of the invention are to improve generally thesimplicity and efficiency of radio receivers equipped with automaticvolume control circuits, and particularly to provide a superheterodynereceiver provided with automatic volume control, accompanied byaninterchannel noise suppressor means, which is not only durable andreliable in operation, but which which we have indicateddiagrammatically sev' eral circuit organizations whereby our invention,may be carried into effect.

In the drawings,

Fig. 1 shows diagranunatically the circuit of a radio receiver embodyingthe present invention,

Fig. 2 is a similar diagram showing a modified form of the invention.

Referring now to the accompanying drawings wherein like referencecharacters designate sim-l ilar elements in the two figures, the radioreceiver shown in Fig. 1 is of the well known superheterodyne type. Thereceiver includes a usual grounded antenna circuit A. coupled to thetunable input circuitcof a radio frequency amplifier tube I, the' latterin turn having its output circuit coupled to the tunable input circuitof a first detector means or tube 2. The usual local oscillator circuitis shown connected to the first 3.0 detector 2 for the impression of theheterodyne frequency upon the iirst detector. This may be accomplishedin any suitable manner. Each of these three aforesaid tunable circuitsincludes a variable tuning condenser, and the rotors of these condensersYare grounded. Any desired type of uni-control tuning mechanism G'may beutilized, the same being shown in dotted lines, for simultaneouslyvarying the rotors of the tuning condensers.

The output circuit 'I of the first detector is iixedly resonant to thedesired operating intermediate frequency. The latter may have a value of175 kilocycles, for example, and the tunable circuits preceding thiscircuit may include any desired means for positively maintaining theintermediate frequency constant. Such a means is not shown, butreference is made to U. S. Patent 1,740,331 to W. L. Carlson, issued onDecember 17, l929.to show such a means for maintaining 5o theintermediate frequency constant throughout thetuning range of thereceiver. The resonant circuit 'I is coupled, as by a transformer M1, tothe resonant 'input circuit of the intermediate frequency amplifier tube4, this input circuit being xedly tuned to the aforesaid operatingintermediate frequency.

The output circuit of the tube 4 includes the resonant circuit 8, xedlytuned to the intermevdiate frequency, which is coupled, as by means of atransformer M2, to the resonant input circuit 9 of the second detector5, the circuit 9 also being xedly tuned to the intermediate frequency,The output of the second detector is transmitted to one, or more,succeeding stages of audio frequency amplification, and a finalreproducer,

through an impedance-transformer coupling network which includes thecoupling reactor I Il. The plate supply to the detector is fed to thecoupling reactor through a lead II which is connected to the highpotential side. of the voltage divider P.

The audio frequency component of the second detector output passesthrough the 0.5 mfd. couplingcapacitor I2, the manual volume control I3being located between the capacitor I2 and the Vaudio frequency couplingtransformer I4.

The manual volume control functions tol reduce the voltage applied tothe primary of the transformer I4, the numeral I5 designating the wellknown manual volume control knob usually disposed on the control panelof the receiver adjacent the tuning control mechanism 6.

The input signal voltage for the intermediate frequency amplifier tube 4is also applied to an automatic volume control amplifier tube I6 due tothe grids of both tubes being coupled together as by means of acapacitor II, the capacitor being shunted to ground on the grid sidethrough a resistor I 7 which may have a value of 2 megohms. The resistorII' functions to provide a grid leak for the tube I 6 to supply bias tothe grid from the selfbias sourceIG indicated. The output voltage of theintermediate frequency amplier tube 4 is applied to the second detector5 through the transformer M2, the latter being sharply tuned to theintermediate frequency. However, the output of the amplifier tube I6 iscoupled to the combined volume control and noise suppressor tube I8through a specially designed coupling network.

This coupling network includes a natural period plate coil L9, whichcoil is connected at one end to the anode of tube I6 and at its otherend to the lead II. Coil L9 is resonant to the intermediate frequencyand broadly so by means of relatively large inductance and smallcapacity. The coil L9 is inductively coupled to a secondary coil Linwhich is sharply tuned to the operating intermediate frequency. The coilL9 supplies the voltage to operate the automatic volume control circuit,and possesses a natural period in order to provide the advantagedescribed in the .said Chittick and Carlson application referred toabove. That is, to provide less selectivity to the automatic volumecontrol circuit than to the second detector circuit. A natural periodcoil of this type has very broad selectivity in itself due to itsinherent loss. The coil L10 supplies the voltage used to operate thenoise suppressor network.

The tubes I, 4 and IE are shown as of the type known by the trade symbol58, and it will be observed that each includes a suppressor grid atcathode potential. The tube I3 is of the type bearing the trade symbol55, and, while conventionally shown, is to be understood as includingthe usual heater type cathode, a control grid and an anode, and twoauxiliary cold electrodes, or anodes, I9, 20. The 55 tube, orduplex-diode triode as it may be aptly termed, is an alternating currentheater type of tube consisting of two diodes and a triode in a singlebulb. In operation, the two diodes and the triode are independent ofeach other except for the common cathode sleeve, which has one emittingsurface for the diodes, and another for the triode. This independence ofoperation permits of unusual flexibility in circuit arrangement anddesign.

For example, in the present arrangement, the electrode 29, controls thefunction of automatic volume control, While the electrode I9 controlsthe noise suppressor action. It is not believed necessary to describethe construction of the tube I8 in detail, since the constructionthereof is not a part of the present invention. It is believedsufficient to point out that the two plates I9 and 29 are disposedaround one end of the common cathode sleeve I9', and that the controlgrid and main anode are concentrically disposed around the cathodesleeve, the anodes I9 and 20 therefore being out'of the mainelectron-stream to the usual control grid and main anode.

The automatic volume control network includes a direct currentconnection between'the 45 grid circuit of each of tubes I,2 and 4 andthe auxiliary electrode 20. Thus, the electrode 2l) is connected to thelow potential side of the grid circuit of 'tube i through a path whichincludes the resistor ZI, having a magnitude of about 10 200,000 ohms,the lead 22, and the resistor R1, having a value oi about 500,000 ohms.The low potential side of the grid circuit of the first detector 2 isconnected to the lead 22 through a path which includes the resistor Rs,having a l5 value of about 100,000 ohms, the lead 23, and the resistorR2, having a value of about 400,000 ohms. The low potential side of thegrid circuit of tube 4 is connected tothe lead 22 through a resistorR13, having a value of about 100,000 20 ohms, the lead 24, the lead 23,and the resistor R2, one side of the resistor R2 being connected toground through a resistor R3, having a value of about 600,000 ohms. 1 i

The resistors R1, R2 and R3 are bypassed to 25 ground notonly for radiofrequency currents but for all signal frequencies through a capacitorC1, the resistor 2i being similarly by-passed for signaland radiofrequency currents by means of a capacitor C2, and the resistors R13 andR9 30 being by-passed to ground for signal and radio frequency currentsby means of the capacitor C3. Direct current blocking condensers C4 andC5 are disposed respectively in the low potential sides of the gridcircuits of tubes I and 2. The 3 the high potential side of the coil Lthrough a path which includes the lead 2t, and the condenser Ce, thelatter having a magnitude of about 300 mmfd. Itis to be clearlyunderstood that magnitudes recited herein are purely illus trative, andmay be freely varied to suit the eX- igencies of a given receiverdesign.

The noise suppressor network is confined to the intermediate frequencycircuits, and is not associated with the audio detector or audiocircuits, thus not only distinguishing the arrange'- ment from systemsemp-loyed in the prior art, but providing an arrangement which resultsin smoother operation and no distortion at the threshold operatingpoint. This network includes a direct connection 25 between the cathodei9 of tube i8 and the grounded leg of the cathode of tube 5, it beingobserved that the grounded leg includes the conventional resistor- 55shunt condenser grid biasing arrangement, a

similar biasing arrangement being employed in the grounded leg of thecathode of tube I0. The low potential side of the sharply tuned coil L10is connected to the lead 25 through a resistor R12 60 having a magnitudeof about 2 megohms, a condenser Cv being connected between one side ofthe resistor R12 and the lead 25, the condenser C1 having a value of0.005 rnfd.y The lead 25 functions to connect the cathode of the sup- 65pressor tube I3 to the cathode of tube 4, establishing the suppressoraction due to the cathode current of suppressor tube I8 flowing throughthe cathode resistor of the intermediate frequency tube 4 and biasingsaid intermediate 70 frequency tube to cut-off when no signal isreceived. The electrode i9 is connectedto the high potential side, ofthe sharply resonant coil- L10, while the control grid'of tube I8 isconnected to the low potential side of the said coil. The

75. triode anode of tube IB is ,connected to 'a point electrode 20 hassignal voltage applied to it from.

26 lon'the divider P through a path which includes the lead 21 andtheon-off switch 28.

The connections to the divider P of certain of the electrode circuitsnecessary to a proper understanding of the invention have only beenshown. Thus, the connections from the screen grids of tubes I and 4 tothe point 29 on the divider P have been shown. Again, the connectionsfrom the anodes of tubes I, 2, A, I6 and 5 to the high potential side ofdivider P, through lead II, have been shown. The cathode of tube I isconnected to ground through a path which includes the lead 30, the lead3|, and the sensitivity control resistor R18, the latter having amagnitude of about 4500 ohms,.an adjustable tap `f being arranged tovary the value of the resistor R18. The cathode circuit of the firstdetector 2 is, also, connected to the lead 3| through a resistor R9,having a value of about 2500 ohms, this resistor R9 functioning to biasthe rst detector to the proper operating point. A resistor R12, of avalue of about 100,000 ohms, is connected between leads 3! and II, andfunctions to provide some bleeder current through the sensitivitycontrol.

`For the purposes of illustration it is pointed out that the resistorportion between the high potential side of the divider P and point 26may have a value of about 3000 ohms; the portion between 26 and 29 mayhave a value of about 600 ohms; the section between point 29 and point+B' may have a value of about 1300 ohms; and, the remaining section toground may have a value of about 2900 ohms. It is to be clearlyunderstood that these values, as well as all other values statedheretofore or hereafter, are merely examples of an actual embodiment. Itis believed that the diagrammatic showing of Fig. l, and the aforegoingdescription, will now render the following explanation of the operationof the invention clearly understandable.

From the secondary of the first intermediate frequency transformer M1the signal voltage is fed to parallel paths. The normal signal pathpasses through the intermediate frequency amplifier tube A1, through thelead 32, to the intermediate frequency output transformer M2. Thecathode of the tube I8 is tied to the cathode of tube 4. The platecurrent through the tube I 8 and the grid bias resistor of tube 4 is ofthe order of ve to ten M. A. before the signal voltage has reached thethreshold operating value. About 45 volts drop exists in the grid biasresistor of tube 4 at this time, which practically cuts off the tube 4,and prevents signals from passing through to the transformer M2. Voltageis also transferred from the secondary of the transformer M1 on tube I6,and is amplied and impressed on the two diode anode electrodes of tubei8.

Coil L9 supplies the voltage to operate the volume control circuit,while coil L supplies that used to operate the suppressor network. Anexamination of this circuit will show that with no signal voltageimpressed on coil L10, no current is rectified in the diode plate IS,and hence the grid of the tube I8 operates at zero bias. The platecurrent is then at a maximum value, approximately 10 M. A., and sincethe cathodes of the tube I8 and the signal channel intermediatefrequency tube 4 are common, the intermediate frequency tube is biasedto cut-oir. This, therefore, prevents signal voltage from reaching thesecond detector through the path including lead 32,`

When the'tuning device Iiv is, however; adjusted to tune in a desiredsignal, the signal voltage is amplified in the automatic volume controlamplifier I6, and impressed on coils L9 and Lio. Ori the positive halfof the signal voltage, the signal is rectified in the suppressor circuitwhich generates Ya negative potential on the grid of the tube I8. Theplate current is thereby reduced to approximately zero, and thisreleases the high bias potential on the signal channel amplifier tube 4.Signal voltage will then be impressed on the second detector.

Automatic volume control bias for the radio frequency, first detectorand intermediate frequency tubes will be generated when the intermediatefrequency voltage on the automatic volume control diode anode 20overcomes and eX'- ceeds the positive potential on the cathode of tubeI8. This bias is approximately 10 volts when the receiver is tuned to asignal. The transformer M2 feeding the second detector includes two highimpedance circuits in order to provide the proper amplification with theincreased'bias resistor in the intermediate frequency cathode circuit.The suppressor circuit including coil L10 is designed to be a sharpcircuit so that the action of the suppressor network comes as near thecenter of the carrier as possible. It is important, therefore, that thislast named circuit be aligned exactly on the center of the intermediatefrequency resonance curve so that the operator of the receiver may heara signal when it is exactly in tune.

The drop across resistors R2 and R3 gives the bias for the radiofrequency stage. The drop across resistor R2 comprises the grid voltagefor the first detector, and intermediate frequency amplifier. As thedrop in these resistors is due to the signal voltage applied to theautomatic volume control tube and this voltage is in turn dependent onthe vbias of the radio frequency, first detector and intermediatefrequency amplier stages, an automatic action is obtained. The reasonfor the greater voltage applied to the radio frequency stage than thatapplied to the first detector and intermediate frequency stages is toprevent overloading of these tubes on the side of a strong carrier.

With the automatic volume control arrangement shown there is no dangerof overloading the second detector, and, accordingly, the manual volumecontrol means may be placed in the audio frequency circuit. Theautomatic volume control plus the special amplifier I6 provides a radiofrequency voltage on the second detector which is substantially constantbetween 9 and 12 volts for a signal of from 10 microvolts to severalvolts. The function of the noise suppressor circuit is to reduce noise,by greatly decreasing the sensitivity of the receiver, when no carrierwaves are being received. The manually operated sensitivity control S isprovided so that the over-all sensitivity of the receiver may beadjusted, thereby eliminating the reception of signals having too greata noise level. This feature operates without introducing distortion, aquality not present in other types of noise suppressor circuits. Themanual sensitivity control S is in the cathode circuit of the radiofrequency and rst detector stages, and

reduces the sensitivity of the receiver by increas-` ing the residualbias on the tube i and the first detector 2. One end of the sensitivitycontrol S has a switch 28 which is provided so that the noisesuppression circuit may be cut out at will.

Under this condition, the full sensitivity of the receiver is obtained.

In other words, the numeral 33 will be understood to designate a commoncontrol mechanism, having a control knob 34 disposed on the receivercontrol panel adjacent knobs I5 and 6, which mechanically couples thevariable tap S and the movable switch arm 28 in such a manner that theswitch 28 is opened at the maximum end of the variable control S. To theoperators ear movement of the knob 34 will sound as if the volumecontrol knob is being actuated to increase the sensitivity of thereceiver. Of course, if the knob 34 is moved towards its maximum, thereproduced noise increases. Hence, it Will be observed that the functionof the control I5 is to vary the sound output of the receiver, withoutregard to reproduced noise; while the function of the control S is tovary the sound output of the receiver with regard to the level ofreproduced noise, and, also, to render the noise suppressor circuiteffective or ineffective at will. The variable resistance Ria controlsthe noise suppression level in that it controls normally negative biason the grid of the radio frequency amplifier and first detector, and,naturally, the greater the normal negative bias on those grids the lessnoise suppression current through tube I8 is necessary to prevent theset from being triggered into operation by the incoming signal. This ismore apparent when it is considered that the radio frequency tube andfirst detector are immediately effective on the incoming signal, whichmust come to a certain level in order to overcome the noise suppressionaction and cause signals to be received.

Fig. 2 shows a modified form of the invention which is diagrammaticallyshown in a highly conventional manner, the circuit energizing sources,for example, being conventionally shown to preserve simplicity ofdisclosure.

The intermediate frequency amplifier tube 4 has its resonant inputcircuit coupled to the source of intermediate frequency energy throughthe coupling transformer M1, while the transformer E designates thecoupling between the output of the tube 4 and the resonant input circuitof the second detector. In this modication the automatic volume controland suppressor circuits are separated. The automatic volume controlarrangement is similar to that shown in the aforementioned co-pendingapplication. That is, the automatic volume control amplifier andautomatic volume ,control tube functions are derived from a single tube40, the control grid of the tube 40 being connected to the highpotential side of the grid circuit of tube 4 through a path whichincludes the lead'4l, and the coupling capacitor 42. The anode of tube40 includes a circuit 43, resonant to the intermediate frequency, thecircuit 43 being coupled, as at D, to a similarly resonant circuit 44disposed in the circuit of the positive electrode 45 of tube 40. Betweenelectrode 45 and the control electrode of tube 40 is disposed a lesspositive electrode 46.

The volume control bias resistors include the resistor R, R and R. Oneside of the resistor R is connected to the negative side of the gridbias source C of the tube 40, the junction of resistors R and R beingconnected by a. lead 50 to the low potential side of the grid circuit oftube 4, as well as to the control grid of tube 60. The anode side ofresistor R" is connected to the radio frequency amplifier grid (notshown) to furnish control bias therefor, and the junc- `and Il).

`tion of resistors R and R" is connected to the will be apparent to oneskilled in the art that oui` first detector grid to furnish control biasfor the latter, the lead Eil furnishing the control bias for theintermediate frequency ampliiier tube 4. The noise suppressor circuit inthis modification includes the ampliiier tube 6D which is coupled, as atC, to the tube TD. This tube is of a type known as the RCA 58.

The auxiliary electrode 'il of tube 'It is connected to the highpotential side of the resonant input circuit l2, while the cathode oftube 10 is connected to the low potential side. The cathode of tube l@is, additionally, connected through a lead i3 to the cathode of tube 4,and functions as the noise suppressor network, and in a manner describedheretofore in connection with Fig. l. Not only is the function of thesuppressor 'lll the same as in Fig. l, but in addition thereto itoperates a power audio amplifier tube 8G which has a 60 cycle currentsource in the plate circuit thereof.` The plate circuit of the tube @ilincludes the primary winding 8l of a step-down transformer 82, thelatter coupling a pilot light to the plate circuit of tube 3i?. Thesecondary winding a3 of the 60 cycle current ransformer 84 is alsoincluded `in the plate circuit of tube 813. The lead 85 connects thecathode side of winding 83 to the cathodes of tubes 4 The negativevoltage on the grid of tube 8B reduces the alternating current in theplate which operates through the step-down transformer 82 to light thepilot light, the latter being an ordinary tuning dial light.

The automatic Volume control operates on the suppressor intermediatefrequency tube $0 so as to hold the voltage to the suppressor controllevel with wide changes of field strength. The suppressor intermediatefrequency transformer C is made very sharply resonant so that whentuning the receiver the suppression will be retained until almost centerresonance. The volume control transformer D is very broad, and thesignal transformer E has medium selectivity. Of course, the connectionsbetween the second detector and the input to tube Bt have been omittedto preserve simplicity of description.

It is believed that the operation of the modification shown in Fig. 2will be clearly understood from the aforegoing description. Briefly,when no signal is impressed on the input circuit of the amplifier tube4, the volume control tube 40 tends to increase the amplification notonly of the intermediate frequency amplifier tube 4, but also theamplification of the first detector and radio frequency tubes. However,in virtue of the signal path 6l, 62 to the control grid of thesuppressor amplifier tube 60, and the action of the 'suppressor tubeTl), the amplifier tube 4 will be vnal energy through the transformer E.Simultaneously, the negative voltage on the grid of tube 3i! isdecreased so that the pilot light becomes brighter, thus visuallysignaling that a signal has been tuned in. Obviously, when the pilotlight vis bright-est, it signifies that the maximum signal is beingimpressed on the input circuit of tube 4. While we have indicated anddescribed several systems for carrying our invention int@ effect, it

invention isby no means limited to the particular lorganizations shownand described, but that many modications may be made without departingfrom the scope of the invention as set forth in the appended claims.

What we claim is:

l. In combination with an amplifier having a signal input circuit and anoutput circuit, a rectifier coupled to said signal input circuit, acontrol tube having its grid connected to said rectifier and its cathodeconnected to the amplifier cathode whereby said amplifier is biased tovcutoff in the absence of signals, and an additional rectiner, coupled tosaid signal input circuit to amplifier for automatically regulating thegain of the amplifier when signals impressed on the amplier input varyfrom a desired level.

2. In combination with an amplier having a signal input circuit and anoutput circuit, a rectier coupled to said signal input circuit, acontrol tube having its grid connected to said rectifier and its cathodeconnected to the amplifier cathode whereby said amplifier is biased tocutoif in the absence of signals, and an additional rectifier, coupledto said signal input circuit to receive signals therefrom, including adirect current connection to a gain control electrode of said amplifierfor automatically regulating the gain of the amplifier when signalsimpressed on the ampliiier input vary from a desired level, saidrectifiers being disposed within said control tube.

3. In combination with an amplifier having a. signal input circuit andan output circuit, a diode rectifier coupled to said signal inputcircuit, a control tube having its grid connected to said rectifierandits cathode connected to the ampliiier cathode whereby said amplifieris biased to cut-off in the absence of signals, and an additional dioderectifier, coupled to said signal input circuit to receive signalstherefrom, including a direct current connection to a gain controlelectrode of said amplifier for automatically regulating the gain of theamplier when signals impressed on the ampliiier input vary from adesired level.

4. In combination with an amplifier having a signal input circuit and anoutput circuit, a diode lier cathode whereby said amplifier is biased tocut-off in the absence of signals, and an additional diode rectifiercoupled, to said signal input circuit to receive signals therefrom,including a direct current connection to a gain control electrode ofsaid amplifier for automatically regulating the gain of the amplifierwhen signals impressed on the amplifier input vary from a delsiredlevel, said rectiers being disposed within said control tube.

5. In combination with an amplier having a signal input circuit and anoutput circuit, a rectiiier coupled to said signal input circuit, acontrol tube having its grid connected to said rectifier and its4cathode connected to the amplifier cathode whereby said amplifier isbiased to cutoff in the absence of signals, and an additional rectifier,coupled to said signal input circuit to receive signals therefromincluding a direct current connection to a gain control electrode ofsaid amplifier for automatically regulating the gain of the amplifierwhen signals impressed on theampliiier;l inputV 'vary from 'a desiredlevel,

f said rectifiers being diodes and being disposed within said controltube, the cathode of the lat- `ter being commonV to both diodes.

6. In combination with an amplifier having a signal input circuit and aload circuit coupled to the output electrodes of thev amplifier, acontrol network for preventing Atransmission of undesired electricimpulses in said input circuit to said Aload circuit, said networkcomprising a diode ycoupled to said signal circuit to provide arectivfied signal output varying directly with the signal intensity insaid input circuit, an electron discharge device having a controlelectrode connected 'to the diode'and output electrodes connected tothesaid input circuit to bias said amplifier to cut off, whereby theamplifier transmission is rendered highly inefcient, when said signalintensity decreases below a'desired level.

7. In combination with anV amplifier having a signal-input circuit and aload circuit coupled to .the output electrodes ofthe amplifier, acontrol network for preventing transmission of undesired electricimpulses ingsaid input circuit to said load circuit, said networkcomprising a diode coupled `to said signal circuit to provide arectified signal output varying directly with the signal-intensity insaidinput circuit, an electronv discharge device having a controlelectrode connected to the diode and output electrodes connected to thesaid input circuit to'bias said amplifier to cut off, whereby vtheamplifier transmission is rendered highly inefficient, 'when said signalintensity decreases belowa desired level and a volume control diode,comprising the cathode of said device and an .auxiliary coldelectrodahavin'g its cold electrode connected through independent signaland direct 'current paths kto 'said signal input circuit.

8. In combination with an amplifier having a signahinput circuit and aload circuit coupled to the output electrodes of the amplifier, acontrol network for preventing transmission of undesired electricimpulses in said input circuit to said load circuit, said networkcomprising a tube having 'disposed' therein a diode coupled to saidsignal 4circuit to provide a rectified signal output vary- -ing directlywith the signal intensity in said input circuit, an electron dischargedevice having a control electrode connected to the diode and outputelectrodes connected to the said input circuit tobias said amplifier toout off, whereby the amplifier transmission is rendered highlyineicient,

.circuit to providea rectified signal output varying directly with thesignal intensity in said input circuit, an' electron dischargev devicehaving a control electrode connected to the diode and output electrodesconnected to the said input circuit to bias said amplifier to cut ofi,whereby the amplifier transmission is rendered highly ineicient, whensaid signal intensity decreases below a desired level.

10. In combination with an amplifier having a signal input circuit and aload circuit including a detector coupled to the output electrodes ofthe amplifier, a control network for preventing transmissionofjundesired electric impulses in said input circuitv to said loadcircuit, said network comprising a diode coupled to said signal circuitto provide a rectified signal output varying directly with the signalintensity in said input circuit, an electron discharge device having acontrol electrode connected to the diode and output electrodes connectedto the said input circuit to bias said amplifier to cut off, whereby theamplifier transmission is rendered highly inefficient, when said signalintensity decreases below a desired level.

ll. A receiver including at least an amplifier and a detector, aresonant signal input circuit connected to the amplifier, a similarlyresonant network coupling the amplifier output electrodes to thedetector input electrodes, a second amplifier having a signal electrodecoupled to said amplier input circuit, a control tube of the typeprovided with at least two independent diode systems and aY triodesystem all having a common cathode, a direct current connection betweenthe common cathode and the first amplifier input circuit, a sharplyresonant circuit connected to one of said diode systems and adapted toreceive amplified energy from the second amplifier, means for connectinga cold electrode of said triode to said one diode, means for connectingthe cold electrode of the other diode to said second amplifier output toreceive signals therefrom, and a direct current connection between saidlast cold electrode and the input circuit of the first amplifier.

12. A receiver including at least an amplifier and a detector, aresonant signal input circuit connected to the amplifier, a similarlyresonant network coupling the amplifier output electrodes to thedetector input electrodes, a second amplifier having a signal electrodecoupled to said ampiifier input circuit, a control tube of the typeprovided with at least two independent diode systems and amulti-electrode system all having a common cathode, a direct currentconnection between the common cathode and the first amplifier inputcircuit, a sharply resonant circuit connected to one of said diodesystems and adapted to receive amplified energy from the secondamplifier, means for connecting a cold electrode of said multi-electrodesystem to said one diode, means for connecting the cold electrode of theother diode to said second amplifier output to receive signalstherefrom, and a direct current connection between said last coldelectrode and the input circuit of the first amplifier, said commoncathode being maintained at a positive potential with respect tosaidlast cold electrode until signals impressed on the first amplifier reacha predetermined intensity level.

13. A receiver including at least an amplifier and a detector, aresonant signal input circuit connected to the amplifier, a similarlyresonant network coupling the amplifier output electrodes to thedetector input electrodes, a second amplifier having a signal electrodecoupled to said amplifier input circuit, a coil having a natural periodin the output circuit of the second amplifier, a control tube of thetype provided with at least two independent diode systems and a triodesystem all having a common cathode, a direct current connection betweenthe common cathode and the first amplifier input circuit, a sharplyresonant circuit connected to one of said diode systems, and adapted toreceive amplified energy from the second amplifier, means for connectinga cold electrode of said triode to said one diode,

means for connecting the cold 'electrode of the other diode to saidsecond amplifier output to receive signals therefrom, and a directcurrent connection between said last cold electrode and the inputcircuit of the first amplifier.

14. A receiver including at least an amplifier and a detector, aresonant signal input circuit connected to the amplier, a similarlyresonant network coupling the amplier output electrodes to the detectorinput electrodes, a second amplier having a signal electrode coupled tosaid amplifier input circuit, a control tube of the type provided withat least two independent diode systems and a multi-electrode system allhaving a common cathode, a direct current connection between the commoncathode and the first amplifier input circuit, a sharply resonantcircuit, coupled to said coil, connected to one of said diode systemsand adapted to receive ampli'ed energy from the second amplifier, meansfor connecting a cold electrode of said multi-electrode system to saidone diode, means for connecting the cold electrode of the other diode tosaid second amplifier output to receive signals therefrom, and a directcurrent connection between said last cold electrode and the inputcircuit of the first amplifier.

15. A receiver including at least an amplier and a detector, a resonantsignal input circuit connected to the amplifier, a similarly resonantnetwork coupling the amplifier output electrodes to the detector inputelectrodes, a second amplifier having a signal electrode coupled to saidamplifier input circuit, a control tube of the type provided with atleast two independent diode systems and a multi-electrode system allhaving a common cathode, a direct current connection between the commoncathode and the first ampliiier input circuit, a sharply resonantcircuit connected to one of said diode systems and adapted to receiveamplied energy from the second amplifier, means for connecting a coldgrid electrode of said multi-electrode system to said one diode, meansfor connecting the cold y electrode of the other diode to the coil insaid second amplifier output to receive signals therefrom, and a directcurrent connection between said last cold electrode and the inputcircuit of the first amplifier.

16. A receiver including at least an amplifier and a detector, aresonant signal input circuit connected to the amplifier, a similarlyresonant network coupling the amplier output electrodes to the detectorinput electrodes, means in the detector output for controlling theenergy output thereof, a second amplifier having a signal electrodecoupled to said amplifier input circuit, a control tube of the typeprovided with at least two independent diode systems and a triodesystemy all having a common cathode, a direct current connection betweenthe common cathode and the rst amplifier input circuit, a sharplyresonant circuit connected to one of said diode systems and adapted toreceive amplified energy from the second ampliiier, means for connectinga cold electrode of said triode to said one diode, means for connectingthe cold electrode of the other diode to said second amplifier output toreceive signals therefrom, and a direct current connection between saidlast cold electrode and the input circuit of the first amplifier.

17. A receiver including at least an amplier and a detector, a resonantsignal input `circuit connected to the amplifier, a similarly resonantnetwork coupling the amplifier output electrodes to the detector inputelectrodes, a second er having a signal electrode coupled to saidamplifier input circuit, a control tube of the type provided with atleast two independent diode systems and a multi-electrode system allhaving a common cathode, a direct current connection between the commoncathode and the rst amplifier input circuit, a sharply resonant circuitconnected to one of said diode systems and adapted to receive amplifiedenergy from the second amplifier, means for connecting a cold electrodeof said multi-electrode system to said one diode, means for connectingthe cold electrode of the other diode to said second amplifier output toreceive signals therefrom, and a direct current connection between saidlast cold electrode and tlie input circuit of the rst amplifier, anamplifier preceding the first amplifier, and means to manually adjustthe sensitivity of the preceding amplier.

18. In combination with an amplifier having a signal input circuit andan output circuit, a rectiiier coupled to said signal input circuit, acontrol tube having its grid connected to said recti- `f lier and itscathode connected to the amplifier cathode whereby said amplifier isbiased to cutofi" in the absence of signals, and an additionalrectifier, coupled to said signal input circuit to receive signalstherefrom, including a direct current connection to a gain controlelectrode of said amplifier for automatically regulating the gain of theamplifier when signals impressed on the amplifier input vary from adesired level, and

an additional tube, including an electrical illumi- 5 nating means andan energizing source therefor in its output circuit, having its inputcircuit connected to the said signal input circuit whereby said sourceis ineffective to energize said illuminating means when said amplier isbiased to cut-01T.

19. In combination with an amplifier having a signal input circuit andan output circuit, a rectifier' coupled to said signal input circuit, a

control tube having its grid connected to said rectiiier and its cathodeconnected to the amplifier cathode whereby said amplifier is biased tocut-off in the absence of signals, and an additional rectifier, coupledto said signal input circuit to receive signals therefrom, including adirect current connection to a gain control electrode of said amplierfor automatically regulating the gain of the amplier when signalsimpressed on the amplifier input vary from a desired level and means forselectively rendering the control tube ineffective to control saidamplier.

20. In a receiver including a radio frequency amplier, a detector, andan audio frequency amplifier, a rectifier arranged to receive signalenergy from said radio amplifier, a direct current connection from therectifier to said radio amplifier to automatically regulate the gainthereof, a second rectier arranged to receive signal energy from saidradio amplifier, a direct current connection from the second rectifierto said radio amplifier to automatically bias the latter to cut-01T whensignals are not received, an electrical illumination device operativelyassociated with the audio ampli-er anode circuit, and a direct currentconnection from the second rectifier to the space current path of saidaudio amplifier to control the intensity of illumination of said device.,i

2l. In a super-heterodyne receiver, a radio frequency amplifier, a firstdetector, an intermediate frequency amplier and a second detector, anautomatic volume control arrangement connected between the input circuitof the intermediate frequency amplifier and the input circuits of theradio frequency amplifier and the first detector, said volume controlarrangement being constructed to vary the gain of said radio frequencyamplifier to a greater extent than that of the ,first detector, and amanual sensitivity control means comprising means for maintaining anormal negative bias on the grids of the radio frequency amplifier andfirst detector, and means for varying the said normal negative bias,means, responsive to a decrease in received signal amplitude below apredetermined amplitude, for

fronde-'ring the'signal transmission to the second detector inefficient,a device for rendering the last means ineffective, and means foractuating the said device upon a predetermined adjustment of said biasvarying means.

22. In a super-heterodyne receiver, a radio frequency amplifier, a firstdetector, an intermediate frequency amplifier and a seco-nd detector, anautomatic volume control arrangement connected between the input circuitof the intermediate frequency amplifier and the input circuits of theradio frequency amplifier and the first detector, and a. manualsensitivity control means comprising means for maintaining a normalnegative bias on the grids of the radiofrequency amplifier and firstdetector, and means for varying the said normal negative bias, abackground noise suppressor arrangement connected between the inputcircuit of said intermediate frequency ampliiier and the cathode circuitof the' latter, a device for rendering the suppressor arrangementinoperative or operative at will, and a common control means formechanically coupling said manual sensitivity control and said device.

23. In a radio receiver, a radio frequency amplifier, a succeedingdetector, an electron discharge tube of the type including a cathode,control grid, a main anode, and a pair of diode anodes disposed adjacentsaid cathode outside the electron stream to said main anode, a signalcoupling path between the input circuit of said amplifier and a tunedinput circuit connected between the said cathode and one of said diodeanodes, a direct current connection between said tuned input circuit andthe input circuit of said amplifier, a signal coupling path between theinput circuit of said amplifier and a diode rectilier circuit comprisingsaid cathode and the other diode anode, a direct current connectionbetween the said diode rectifier circuit and the input circuit of saidamplifier, a direct current path between said main anode and the saidcathode, and a connection between the said control grid and said tunedinput circuit.

24. In a radio receiver, a radio frequency amplifier, a succeedingdetector, an electron discharge tube of the type including a cathode,control grid, a main anode, and a pair of diode anodes disposed adjacentsaid cathode outside the electron stream to said main anode, a signalcoupling path between the input circuit of said amplifier and a tunedinput circuit connected between the said cathode and one of said diodeanodes, a direct current connection between said tuned input circuit andthe input circuit of said amplifier, a signal coupling path between theinput circuit of said amplifier and a diode rectifier circuit comprisingsaid cathode and the other diode anode, a direct current connectionbetween the said diode rectiiier circuit and the input circuit of saidamplifier, a direct current path between said main anode and the saidcathode, a connection between the said control grid and said tuned inputcircuit, and a signal coupling path between the anode circuit of saidamplifier and said detector, the signal coupling path to the first diodeanode and the detector being relatively more sharply tuned than thesignal coupling path to the said diode rectifier circuit.

25. Radio receiving apparatus comprising, in combination, signalselecting means turnable to receive any signal of a desired frequency ina predetermined signal frequency range, a demodulatc-r coupled totheselecting means, an audio amplifier following said demodulator, lightindicating means connected to said amplifier for producing variations inlight in accordance with the average current fiowing through theamplifier, and means for automatically controlling the current flowthrough said amplifier in response to a variation in amplitude of areceived signal.

26. Radio receiving apparatus comprising, in combination, signalselecting means tunable to receive any signal of a desired frequency ina predetermined signal frequency range, an amplifier following saidmeans, light indicating means connected to said amplifier for producingvariations in light in accordance with the average current iiowingthrough the amplifier, means for automatically controlling the currentiiow through said amplifier in response to a variation in amplitude of areceived signal, a detector disposed between the selecting means and theamplifier, and said amplifier being connected to amplify the audiocomponent of the detected signal current.

27. Radio receiving apparatus comprising, in combination, signalselecting means tunable to receive any signal of a desired frequency ina predetermined signal frequency range, a demodulator coupled to theselecting means, an audio amplifier following said demodulator, lightindicating means connected to said amplifier for producing variations inlight in accordance with the average current flowing through theamplifier, means for automatically controlling the current flow throughsaid amplifier in response to a variation in amplitude of a receivedsignal and independent means for automatically regulating theamplification of .a selected signal prior to impression upon saidamplifier.

28. In combination, in a radio receiver, a signal amplifier, means fordetecting the amplified signal, an automatic gain control circuit oper-.atively associated with the amplifier for regulating the gain thereofin a sense to maintain the signal carrier amplitude at the detectingmeans substantially constant, noise suppressor means responsive to apredetermined decrease in received carrier .amplitude for substantiallydecreasing the signal transmission through the receiver prior to saiddetecting means, manually adjustable means for varying the gain of theamplifier independently of the said gain control circuit, and.additional means for rendering the noise suppressor means inoperative,said additional means being mechanically coupled with said manuallyadjustable means to function at the minimum gain adjustment point ofsaid manually adjustable means.

29. In a high frequency signal reception system of the type comprising ademodulator, a high freiol quency signal amplification network feedingsignals to the demodulator, a demodulated signal transmission networkcoupled to the demodulator output, means, responsive to received signalamplitude increase, for automatically decreasing the transmission ofsignals to the demodulator, noise suppressor means independent of thefirst means for automatically decreasing the signal transmission to thedemodulator upon a decrease of the received signal amplitude below apredetermined intensity level.

30. In a high frequency signal reception system of the type comprising ademodulator, a high frequency signal amplification network feedingsignals to the demodulator, a demodulated signal transmission networkcoupled to the deinodulator output, means, responsive to received signalamplitude increase, for automatically decreasing the transmission ofsignals to the demodulator, noise suppressor means independent of thefirst means for automatically decreasing the signal transmission to thedemodulator upon a decrease of the received signal amplitude below apredeteimined intensity level, a manually adjustable device forregulating the signal transmission einciency of the amplificationnetwork, a manually adjustable device for controlling the demodulatedsignal transmission eiiciency. l

31. In a high frequency signal reception system of the type comprising ademodulator, a high frequency signal amplication network feeding signalsto the demodulator, a demodulated signal transmission network coupled tothe demodulator output, means, responsive to received signal amplitudeincrease, for automatically decreasing the transmission of signals tothe demodulator, noise suppressor means independent of the first meansfor automatically decreasing the signal transmission to the demodulatorupon a decrease of the received signal amplitude below a predeterminedintensity level, a manually adjustable device for regulating the signaltransmission einciency of the amplification network, a manuallyadjustable device for controlling the demodulated signal transmissionefficiency, and means for rendering the noise suppressor meansineffective.

32, In a high frequency signal reception system of the type comprising ademodulator, a high frequency signal amplification network feedingsignals to the demodulator, a demodulated signal transmission networkcoupled to the demodulator output, means, responsive to received signalamplitude increase, for automatically decreasing the transmission ofsignals to the demodulator, noise suppressor means independent of thefirst means for automatically decreasing the signal transmission to thedemodulator upon a decrease of the received signal amplitude below apredetermined intensity level, and said suppressor means having asharper signal selectivity characteristic than said rst means.

33. In a high frequency signal reception system of the type comprising ademodulator, a high frequency signal amplification network feedingsignals to the demodulator, a demodulated signal transmission networkcoupled to the demodulator output, means, responsive to received signalamplitude increase, for automatically decreasing the `transmission ofsignals to the demodulator, noise suppressor means independent of therst means for automatically decreasing the signal transmission to thedemodulator upon a decrease of the received signal amplitude below apredetermined intensity level,

said amplification network including at least one amplier tube, and saidsuppressor means including a direct current connection Ato a gaincontrol electrode of the tube.

34. In a high frequency signal reception system of the type comprising ademodulator, a high frequency signal amplification network feedingsignals to the demodulator, a demodulated signal transmission networkcoupled to the demodulator output, means, responsive to received signalamplitude increase, for automatically decreasing the transmission ofsignals to the demodulator, noise suppressor means independent of thefirst means for automatically decreasing the signal transmission to thedemodulator upon a decrease of the received signal amplitude below apredetermined intensity level, a light emitting device electricallyassociated with the demodulated signal network, and means responsive tosaid signal amplitude decrease for decreasing the light emitted by thedevice.

35. In a high frequency signal receiver of the type comprising adetector, a tunable high frequency amplier preceding the detector andfeeding it, an audio amplifier fed by the detector, a tuning indicatorlight emission device operatively associated with the audio amplifierspace current path, a source of alternating current coupled to the saidspace current path to energize the light device, and means, responsiveto amplitude variations at the high frequency amplier, for controllingthe light emitted by the device.

WENDELL L. CARLSON. LOREN R. KIRKWOOD.

